The accuracy of two 4-hour identification systems for anaerobes, the AN-IDENT (Analytab, Products, Plainview, NY) and the RapID ANA (Innovative Diagnostic Systems, Inc., Atlanta, GA) was compared with that of the API 20A system (Analytab Products). A total of 268 clinical isolates were tested. The overall accuracies at the genus and species level for the 3 systems were: API 20A, 74 and 64%; AN-IDENT, 82 and 73%; and RapID ANA, 77 and 73%. Improved identification of anaerobes with the AN-IDENT and the RapID ANA system was observed for isolates of the genera Fusobacterium, Clostridium (other than C. perfringens), and Peptostreptococcus.